The invention generally relates to the application of crosswires to a tension focus mask for use in color picture tubes and, more particularly, to a method and apparatus of protecting the edges of mask frame assembly from damage during handling and providing an integral beam shield as well as stabilize the edge strands.
A color picture tube includes an electron gun for forming and directing three electron beams to a screen of the tube. The screen is located on the inner surface of the faceplate of the tube and is made up of an array of elements of three different color-emitting phosphors. An aperture mask, which may be either a shadow mask or a tension mask, is interposed between the electron gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. A shadow mask is a thin sheet of metal, such as steel, that is contoured to somewhat parallel the inner surface of the tube faceplate. A shadow mask may be either domed or tensioned. A type of tension mask, called a tension focus mask, comprises two sets of conductive elements that are perpendicular to each other and separated by an insulator. Two different voltages are applied to the two sets of elements to create quadropole focusing lenses in each of the mask opening, which form a focus mask. The mask openings are defined by the rectangular space between adjacent vertical lines and adjacent horizontal lines. Generally, in a tension focus mask, a vertical set of conductive lines or strands is under tension and a set of horizontal conductive elements sometimes known as crosswires overlies the strands.
In cathode ray tubes containing tension focus masks, the spatial integrity of the strands and crosswires is critical. The crosswires and strands must not move from their respective positions during tube operation or during tube fabrication. Any such motion of the crosswires could impact the mask strands causing electron beams to misregister with the phosphor elements, during tube operation. It is therefore desirable that the mask structural elements, especially those used to terminate the crosswires, must be rigid.
The present invention provides an apparatus and method of constructing a rigid busbar for the purpose of preventing damage to a tension focus mask due to handling during the manufacturing process. The apparatus includes a mask frame assembly having a set of short sides constructed by robust steel structural members. The short sides are formed from a base segment formed of a stainless steel 90xc2x0 extruded angle shape having two respective ends. The 90xc2x0 extruded base segment forms the bottom and side rail of the short side of the mask frame assembly. This side rail is attached on each of its respective ends to two square tubes that form the long sides of the rectangular mask frame assembly. Above the stainless steel side rail is another larger side rail formed of cold rolled steel in the shape of an angle attached on each end to the square tubes. A set of arched cantilevers are also attached to the ends of the side rails above the point where the square tube is joined to the side rail.
The cantilevers support a tension mask that is welded to each of the cantilevers and whose strands are parallel to the short sides of the mask frame assembly.
Along the outsides of the steel side rails is attached an insulating strip. A set of bus bars are then attached to the outside of the insulating strips. A plurality of crosswires are laid perpendicular to the mask strands and attached on each end to the bus bars.